IDeAs - Ground Source Heat

Daylighting	Natural ventilation/radiant heat	Ground Source Heat	Integrated design
Advanced Glazing & Insulation	Energy-saving office equipment	Renovation Not Green-field
Energy-efficient lighting	Energy Control & Monitoring	Building-integrated photovoltaics

An electric, ground-source heat pump produces both chilled water and hot water efficiently to lower energy use in accordance with net zero energy and zero carbon emission philosophy of this building. The geothermal system takes advantage of what the earth naturally provides - a constant below ground temperature of about 10 degrees Celsius.

The natural HVAC system relies on pipes laid under the open landscape area of the 3,160 square meter site.

	Ground-Source Heat Pump Chilled or hot water is provided both to the radiant slab and the dedicated outside air handler via a heat pump with a cooling energy efficiency ratio (EER) rating of over 19. High pumping efficiencies are gained by the design of a low-pressure drop piping system coupled with open-ported ball type control valves. The fully electronic control system accurately controls the floor cooling flow rates and temperature to provide the maximum performance for the lowest pumping power and warmest chilled water temperatures. Pump speeds are kept at their lowest demand speed using power inverter technology based on actual demand.
	Outside-Air Handler One of the challenges of this system is avoiding floor condensation. This is mitigated by automatic dehumidification by the air handler. If humidity is detected, chilled water and concurrent condenser water is applied for temperature control via a pair of dual coils in the air handler.
	Landscape Area The earth under the landscaping serves as the ground source heat sink for energy absorption and rejection and storage for the heat pump system. It’s trenched with a field of PEX piping six feet and four feet deep to provide an energy storage field. System efficiencies are increased by providing a relatively steady temperature heat sink for the heat pump system rather than using outside air to absorb and reject heat to where temperatures vary far more widely. The thermal storage capacity of the earth also allows for high efficiency between heating and cooling modes of operation that alternate from morning to afternoon.
	Creekside Landscape The native soil had enough clay that was suitable for the energy transfer. Otherwise concrete or other dense material would have had to be imported. Monitoring the backfill and compaction process to avoid air pockets around the pipe was critical to the systems performance. The underground piping was stacked at 6 feet and 4 feet deep to minimize its footprint. At 6 feet on center and 2 feet wide, the trenching process was extremely challenging. Soil conditions changed the closer the trenches got to the creek bed. Hopscotching became necessary to maintain the integrity of the trench banks.